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The pH sensor of the plant K+-uptake channel KAT1 is built from a sensory cloud rather than from single key amino acids

  • The uptake of potassium ions (K+) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (approximately 2-2.5 pH units) is perceived by voltage-gated inward potassium channels (K-in) that then can open their pores with lower energy cost. The sensory units for extracellular pH in stomatal K-in channels are proposed to be histidines exposed to the apoplasm. However, in the Arabidopsis thaliana stomatal K-in channel KAT1, mutations in the unique histidine exposed to the solvent (His(267)) do not affect the pH dependency. We demonstrate in the present study that His(267) of the KAT1 channel cannot sense pH changes since the neighbouring residue Phe(266) shifts its pK(a) to undetectable values through a cation-pi interaction. Instead, we show that Glu(240) placed in the extracellular loop between transmembrane segments S5 and S6 is involved in the extracellular acid activation mechanism. Based on structural models we propose that this region may serve as a molecular link between the pH-The uptake of potassium ions (K+) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (approximately 2-2.5 pH units) is perceived by voltage-gated inward potassium channels (K-in) that then can open their pores with lower energy cost. The sensory units for extracellular pH in stomatal K-in channels are proposed to be histidines exposed to the apoplasm. However, in the Arabidopsis thaliana stomatal K-in channel KAT1, mutations in the unique histidine exposed to the solvent (His(267)) do not affect the pH dependency. We demonstrate in the present study that His(267) of the KAT1 channel cannot sense pH changes since the neighbouring residue Phe(266) shifts its pK(a) to undetectable values through a cation-pi interaction. Instead, we show that Glu(240) placed in the extracellular loop between transmembrane segments S5 and S6 is involved in the extracellular acid activation mechanism. Based on structural models we propose that this region may serve as a molecular link between the pH- and the voltage-sensor. Like Glu(240), several other titratable residues could contribute to the pH-sensor of KAT1, interact with each other and even connect such residues far away from the voltage-sensor with the gating machinery of the channel.show moreshow less

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Metadaten
Author:Wendy Gonzalez, Janin Riedelsberger, Samuel E. Morales-Navarro, Julio Caballero, Jans H. Alzate-Morales, Fernando D. Gonzalez-Nilo, Ingo DreyerORCiDGND
DOI:https://doi.org/10.1042/BJ20111498
ISSN:0264-6021 (print)
Parent Title (English):The biochemical journal
Publisher:Portland Press
Place of publication:London
Document Type:Article
Language:English
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Tag:Arabidopsis thaliana; KAT1; channel protein structure; channel protein-proton interaction; pH regulation; potassium chanel
Volume:442
Issue:7
Pagenumber:7
First Page:57
Last Page:63
Funder:DAAD-CONICYT (Servicio Aleman de Intercambio Academico-Comision Nacional de Investigacion Cientifica y Tecnologica); Fondo Nacional de Desarrollo Cientifico y Tecnologico (Chile) [11100373]; Abate Molina Excellence Award; Deutsche Forschungsgemeinschaft [DR 430/8]; Heisenberg fellowship; Max-Planck Research School; CONICYT (Comision Nacional de Investigacion Cientifica y Tecnologica)
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Biochemie und Biologie
Peer Review:Referiert